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Pyrethrum (<i>Tanacetum cinerariifolium</i>) is a perennial plant grown commercially for the extraction of the natural insecticide, pyrethrin, from its flowers. The Australian pyrethrum industry supplies more than 60% of the world’s pyrethrin requirements. Ray blight is a major threat to pyrethrum production in Australia, capable of causing complete yield loss. The disease appeared in Tasmanian fields in 1995 and the causal agent was identified as <i>Phoma ligulicola</i> var. <i>inoxydabilis</i>. Further studies on the morphology and biology of the fungus revealed some divergence from the published descriptors of the type strains, which cast some doubts on its taxonomy. The aim of this study was to reassess the taxonomy of the pathogen. Australian and overseas isolates from pyrethrum and other <i>Asteraceae</i> were compared to the type strains of the ray blight pathogen based on morphological characters and multi gene phylogeny of LSU, ITS, TUB, ACT and EF sequences. Results showed that ray blight of <i>Asteraceae</i> is caused by multiple species of the genus <i>Stagonosporopsis</i>. The type strains of the ray blight pathogen, previously known as var. <i>inoxydabilis</i> and var. <i>ligulicola</i>, were elevated to species <i>S. inoxydabilis</i> and <i>S. chrysanthemi</i>, respectively. The pathogen associated with ray blight of pyrethrum in Australia was re-classified as a new species, <i>S. tanaceti</i>. This finding highlights the need for further studies into the biology of the pathogen since it may have quarantine and epidemiological implications for the industry.<p><p>Keywords: Fungus